Gas or air turbine starters have been used in many applications for purposes of providing torque to an engine, such as a main propulsion engine of an aircraft. Normally, the gas turbine starter is provided with a flow of air from some source, such as a bleed conduit from the main engine or an auxiliary power unit.
For instance, a frequent method of starting aircraft prime propulsion gas turbine engines is by means of a small auxiliary power unit providing compressed (bleed) air to an accessory drive gearbox mounted air turbine starter. The auxiliary power unit may be carried on-board, or mounted externally on ground support equipment. The majority of such auxiliary power units deliver a bleed pressure of approximately 4.0 psi at standard day conditions, as constrained by oil auto-ignition temperature limits no higher than 450.degree.-550.degree. F. for most commercial aircraft applications.
Requirements for in-flight cross-bleed starting of military propulsion engines at higher Mach numbers have necessitated accommodating bleed air duct internal temperatures of up to approximately 1200.degree. F. In accommodating these higher bleed air duct internal temperatures, lines have had to be extensively insulated to maintain tolerable external surface temperatures.
This invention is directed to an improved system which significantly increases the output of the gas turbine starter by providing an additional or supplemental in-flow of hot gas to the starter, principally from a combustor means.